The present invention relates to a field emission element for allowing electrons to be emitted from a surface of a metal or a semiconductor by utilizing a field emission phenomenon, a method of fabricating the element, and a field emission display using the field emission element.
A field emission element, which allows electrons to be emitted from a solid due to no thermal excitation, is typically used for an electron source for drive of a FED (Field Emission Display).
As such a field emission element, there has been known a Spindt type in which a cold cathode for emitting electrons is formed into a pyramid or cone shape.
A method of fabricating the related art Spindt type field emission element will be described with reference to FIGS. 27A to 27C and FIGS. 28A and 28B.
As shown in FIG. 27A, a cathode electrode 101 made from chromium (Cr), niobium (Nb), tantalum (Ta), tungsten (W) or the like is formed into a specific pattern on a glass substrate 100. A gate electrode 103 made from Cr, Nb, Ta, W or the like is formed into a pattern crossing the pattern of the cathode electrode 101 on the cathode electrode 101 through a silicon oxide (SiO.sub.2) film 102. A resist film 104 is formed on the gate electrode 103, and an opening 105 is formed in the resist film 104 at a specific position by photolithography. Then, the gate electrode 103 is etched using the resist film 104 as an etching mask, to form an opening 106 having a diameter of about 1 .mu.m in the gate electrode 103.
As shown in FIG. 27B, the SiO.sub.2 film 102 is etched through the opening 106 of the gate electrode 103, to form a through-hole 107 in the SiO.sub.2 film 102. At this time, the SiO.sub.2 film 102 is side-etched, so that as shown in FIG. 27B, the through-hole 107 is slightly wider than the opening 106 of the gate electrode 103.
As shown in FIG. 27C, the resist film 104 is removed and a peeling layer 108 made from aluminum (Al) or the like is formed on the gate electrode 103 by oblique vapor-deposition.
As shown in FIG. 28A, a metal material such as molybdenum (Mo) or W or a semiconductor material such as diamond is vapor-deposited in the direction substantially perpendicular to the substrate 100, to form a vapor-deposition layer 109 on the gate electrode 103, and also to form, through the opening 106 of the gate electrode 103, a cathode cone (or emitter cone) 110 made from the above material on a portion of the cathode electrode 101 exposed in the through-hole 107 of the SiO.sub.2 film 102.
Then, as shown in FIG. 28B, the peeling layer 108 is removed by dissolution, to peel the vapor-deposition layer 109 on the gate electrode 103.
With these steps, a Spindt type field emission element is formed in which the cathode cone 110 as a field emission source is provided in the fine opening 106 formed in the gate electrode 103.
The field emission element thus formed is used as an electron source for drive of a display such as a FED.
For example, as shown in FIG. 29, when a specific voltage Vg is applied between the gate electrode 103 and the cathode electrode 101 of one selected from the field emission elements arranged in a matrix pattern corresponding to a matrix pattern of pixels, there occurs concentration of an electric field at a peak portion of the cathode cone 110. This allows electrons to be emitted from the peak portion of the cathode cone 110. The electrons thus emitted are accelerated by a voltage Va applied between the gate electrode 103 and a transparent electrode 111 as an anode, and then collide with a phosphor screen 112, thereby allowing light emission of the phosphor screen 112.
In the above-described related art Spindt type field emission element, field emission characteristics thereof are largely affected by a distance between the opening 106 of the gate electrode 103 and the peak portion of the cathode cone 110. On the other hand, such a distance is dependent on in-plane uniformity of thickness of the vapor-deposition film 109, and more specifically, the distance varies depending on the amplified non-uniformity of the film thickness. Accordingly, for example, in order to fabricate a display having uniform field emission characteristics, the above step of forming the vapor-deposition layer 109 is required to be carried out such that the vapor-deposition film 109 is uniformly formed at a high accuracy over the entire surface of the substrate.
However, it has been very difficult to form the vapor-deposition film 109 uniformly at a high accuracy over the entire surface of a large-area substrate, and therefore, it has failed to realize a large-area display with a high quality.
Another problem of the related art Spindt type field emission element is that the fabricating yield has been poor because of contamination of the element occurring upon peeling of the vapor-deposition layer 109.